The present invention relates to the actuation of a slat in an aircraft wing running on rails arranged in the front portion of wing of an aircraft. Devices to which the invention pertains include structure wherein a slat is for instance held by means of thrust rods which are linked to and operated by cranks by means of which the slat can be extended and retracted. Usually there are multiple slats driven by a central drive facility, a common transmission path and drive facilities either in a centralized or a decentralized fashion so as to actuate the various slats along the leading edge of the wing.
Slats are used in wings of aircraft in order to improve the lift-to-drag relationship, particularly during critical phases of flight. These slats are usually extended or retracted by means of spindle drives cooperating with levers, cranks and so forth. Stationary rollers run on a curved track which is fastened to the slat. The slat and the actuation including crank drives, thrust rods, rails, etc. permit movement of the slat along a circular track but will lift off the rigid nose of the wing, as the slat moves in upstream or forward direction. A gap continuously opens between the slat and the wing nose proper until a maximum extension is obtained, wherein that gap has also maximum value.
U.S. Pat. No. 4,437,631, corresponding to German Pat. No. 2,916,040, includes a wing with movable slats which is driven through thrust rods and crank drives; different arrangements are driven through a common drive shaft, and the particulars of that adjustment includes a crank arm connected to be driven by a gear and a rod is linked with one end directly to the crank, the other end is pivotally linked to the slat, and there is a cover on the thrust rod extending for the length and completing the wing surface when the slat is held in a retracted position. An arc-shaped guard rail is connected to the slat and a guide structure is in running engagement with the rail and is connected to the wing to obtain the drive along a pre-described path.
A very important aspect of that patent is to make sure that there is aerodynamic continuity. It was found, however, that a certain problem arises for a slat drive of the type of that patent in that for take-off and landing, as well as climbing, the dispositions of the slat are basically quite similar, which means that right from the beginning of the extension, the slat lifts off the nose of the wing. Landing and take-off, however, require different aerodynamic considerations. For example, for takeoff and climbing, there is supposed to be an optimum relationship between lift and drag, i.e. the lift is supposed to be high, and the drag is supposed to be low. During landing, the situation is actually the reverse.